<html>
<title></title>

<style>
.container{
position:absolute;
background:#000;
border:6px;
width:400px;
height:400px;
margin-left:250px;
margin-top:50px;
}

#content{
width:350px;
margin-left:25px;
margin-top:25px;
background:#fff;
height: 350px;
}

#start{
background:#f00;
margin-top:360px;
}

#end{
background:#f00;
}
</style>

<div class='container'>
	<div id='content'></div>
</div>

<button id='start'>Start</button>
<button id='end'>End</button>

<script>
window.onload=function(){
	var btn_start = document.getElementById('start');

	btn_start.onclick=function(){
		this.style.display='none'
	}

	var btn_end = document.getElementById('end');

	btn_end.onclick=function(){
		btn_start.style.display='block'
	}


}
</script>
</html>
